General procedure for the synthesis of ethyl 4,4-dimethoxy-but-2-enoate from triethyl phosphonoacetate and glyoxal dimethyl acetal: In a solvent mixture of 210 mL of tetrahydrofuran and 30 mL of water, potassium carbonate (16.5 g, 120 mmol), glyoxal dimethyl acetal (60% wt. aqueous solution, 15 mL, 100 mmol) and triethyl phosphonoacetate (20 mL, 100 mmol). The reaction mixture was stirred at room temperature for 4 hours. After completion of the reaction, the mixture was poured into ether (200 mL) and washed with saturated aqueous sodium chloride. The organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product ethyl 4,4-dimethoxy-but-2-enoate as a yellow oil (15.8 g, 90% yield). The structure of the product was confirmed by 1H-NMR (300 MHz, CDCl3): δ 6.77 (dd, J = 15.9, 4.0 Hz, 1H), 6.13 (dd, J = 15.9, 1.4 Hz, 1H), 4.95 (dd, J = 4.0, 1.4 Hz, 1H), 4.22 (q, J = 7.1 Hz, 2H), 3.34 (s , 6H), 1.30 (t, J = 7.1 Hz, 3H).
